The zoning ordinance regulates building size and density in three ways: through floor area ratio (FAR), “minimum lot area per unit” (MLA, a backwards way of saying dwelling units per acre), and through various setback regulations. Yet these don’t follow a linear relationship at all; instead, the interaction between FAR maximums and MLA minimums encourages larger buildings with fewer apartments in lower-density districts, and more apartments per building in higher-density districts.

What this graph shows is: If I have a standard city lot in a given zoning district, and I build the biggest possible building with the most possible units, how large would those units be? The answer varies tremendously across the city, from a low of ~600 square feet in high-density districts like RM-6 and DR-7, to “impossible” in the lowest-density districts (note 1).

Most of the city’s neighborhoods, from the Bungalow Belt through the Zone of Two-Flats (mostly zoned RS-3) and into the Zone of Three-Flats (mostly RT-4), is zoned for the lowest-density (left-most) third of this graph. From RM-4.5 on down, the average apartment that can be built at the maximum density must be 1,250 square feet or larger (the size of a large two-bedroom apartment). Sure, you could build studio and one-bedroom apartments, but then you’d have to build huge three- and four-bedroom apartments, too.

Only for RM-5 and above, high-density zoning classifications pretty much only found in a narrow band along the lakefront, do the average apartment sizes permitted begin to dip into one-bedroom territory.

Someone who wishes to build new smaller apartments, like one-bedrooms or studios, in order to accommodate shrinkinghouseholds can only do so in neighborhoods like Lakeview or Logan Square by either (a) under-building the FAR, at a considerable opportunity cost, or (b) getting rezoned to a denser category. Anyone who goes the latter route might as well build a lot bigger and higher, too.

Methodology notes:

I assumed a standard 25′ x 125′ (3,125 sq. ft.) city lot. In RS-1 and RS-2, you cannot build on a lot that small, hence those values are excluded.

The MLA chosen is the number specified for efficiency apartments, a distinction made in higher-density districts which would skew their figures down.

“BCD” here refers to mixed-use zones that can be designated Business, Commercial, or Downtown depending on the use. What’s important for these purposes is the numeral in the zone name, which defines the density allowed. These zones all permit (and indeed, require) substantial amounts of commercial floor space, which counts against FAR but not MLA; for these zones, I assumed an apartment building with 0.5 FAR of commercial space, and the rest residential. This skews the figures upwards for downtown districts, where one would reasonably expect more than 0.5 FAR of commercial space.

No less an authority on great streets and great cities than Holly Whyte, guiding spirit of the Project for Public Spaces, wrote in City: “But the most fascinating of Tokyo’s streets are its ordinary ones. Mile after mile, they are consistently more interesting than ours. In the Shinjuku district there are more streets to savor than in most U.S. cities put together, and for sheer sensory impact there is nothing to match its back alleys…” (And Whyte’s comparison set was NYC in the 1980s, which hardly lacked for “interesting” streets that packed in “sensory impact.”)

Tokyo disabused me of any notion that classical architecture was integral to creating walkable, human-scaled places, or that newness per se is the problem. Japanese cities show that fascinating places can exist with mediocre 20th-century architecture. And because they’ve shown that it’s possible to build fantastic, prosperous, massive, and efficient cities in the 20th century, they’re much more powerful examples for city-builders in our time than European antiquities.

Here’s just a random intersection I walked through near Fudomae station, southwest of the city center and outside the Yamanote Line “beltway,” where a friend of mine happened to let me stay in her inexpensive flat. Yet it’s quiet, livable, affordable, fascinating to walk around, and completely illegal in America due to its narrow streets, mixed uses, Byzantine street pattern, high lot coverage, and high density — in other words, its small scale.

Many smaller buildings will create a much more lively streetscape, and more opportunities for cool urban spaces, than fewer but larger buildings. The critical deficiency in American cities, by comparison, is not limited to fixing a single profession, like architecture or even engineering. Rather, our entire system is tilted towards gigantism: our suburban-era parcel sizes, our High Modern-era zoning (which almost require large buildings), our mortgages, our street design manuals, our nonsensically upside-downparking requirements.

If the stupendous urbanism yields such terrific results in the hands of ordinary architects, it becomes sublime in the hands of masters like Tadao Ando.

The ULI Case Study that I wrote about Sofia Lofts, a 17-apartment development in a neighborhood in eastern San Diego, was recently posted. I was particularly intrigued by how the developer/architects used shared space to maximize usable open space while meeting the letter of the law with regard to parking requirements:

For the balance of the 21 [parking] spaces planned, six more garages are accessed via the courtyard. The plans show seven more spaces within the courtyard itself, immediately in front of the garages — but to keep the space inviting, the spaces in the courtyard are off limits for tenant parking. It’s a small net loss for NDD, which discounts the rent for some tenants who forgo on-site parking, but results in a common area that looks like an expansive garden, rather than a parking lot.

The materials used within the courtyard were also chosen to make the garden feel like a place where cars just happen to be allowed. Part of the driveway near the alley is paved with concrete, but the center of the property is covered in pea-sized gravel. The texture of the gravel slows down cars to walking speed, adds visual and auditory interest, and permits rainwater to filter through. Its inspiration comes from a house in Italy that the Nakhshab family lived in; as Soheil recalls, “The courtyard we would always play in had that type of gravel, and we are seeing the tenants’ children doing the same thing.”

Here’s my old block in Wicker Park (and namesake for this blog): the 2100 block of West North Avenue. It’s also an interesting illustration of how Chicago’s 1957 zoning ordinance made courtyard apartment buildings illegal — even though this eminently livable, passively vented building type defines high-density Chicago neighborhoods like Rogers Park and South Shore.

What did courtyards in were backyards. The 1957 ordinance (mildly updated since) requires a 30-50′ rear yard for residential units in all but the densest of downtown zones; functionally, this is where the garage went. This mandate shifted open space to the rear of the lot, and the entire point of a courtyard building is that the open space is consolidated at the center of the lot.

The 1911 C-shaped courtyard shown at lower right has minimal setbacks along the sides and rear, which results in a generous central courtyard. The 1901 3-shaped courtyard at upper left was required (by a subdivision-specific covenant and by a ‘L’ line easement) to retain front and rear setbacks, and as a result its courtyard shape is so constrained as to be almost illegible. The new buildings at lower left were required to have a rear setback (the ones at far left got a slight variance) and thus consolidate their open space at the front and rear of their lots, to the great detriment of the tiny sliver of open space that the architect sought to insert in the middle.

Other contributing factors to the demise of courtyard apartments include:

Parking requirements, which are difficult but not impossible to accommodate in basements. The large courtyard shown here is raised, and could have been built with parking underneath.

The fashion for high-rises and for deeper floorplans in general, fed by postwar technological changes — cheaper steel and concrete, improved lighting, air conditioning, elevators, etc.

By the time 1929 came around, appropriate sites for courtyard buildings, which required contiguous lots zoned for medium density (at the time, Chicago had three density districts, although then as now the low-density district was pretty capacious). In 1945, when construction resumed, the city’s builders had shifted their attention away from the relatively built-up lakefront.

The entrance to Hong Kong’s airport express train is somewhere within this mall. The cross-border bus terminal entrance is somewhere else entirely, and the actual “public” spaces are completely dispiriting.

When I was a small child, John Portman-style complexes were architecture’s futuristic vision: Someday, we’d all live in hermetically sealed downtown compounds of office and hotel skyscrapers set atop multi-story podiums.

My family stayed in several of these hotels on trips; sometimes, my mom would tell me about how she, as a child in Hong Kong, had dreamed of a city of skyscrapers and layers of indoor shops, all suspended above grade so that buses, boats, and cars could fill the ground plane.

That hyper-dense Modernist vision eventually came to pass in much of central Hong Kong, fed by not only its unique geography but also by its unique private-provision model for both rail and property. There’s danger, it turns out, in putting developers in charge of your rail stations; the “gift horse” of free infrastructure comes with strings attached.

When private firms are put in charge of designing pedestrian circulation networks, they will place their values — primarily shuffling eyeballs past storefronts — over the public’s need for legible, direct links from A to B. The tremendously high value of rail access behooves developers to elbow their way closer to the station; the location imperative isn’t to be near transit, it is to be at transit; to make it not just easy, but necessary to traverse their property. And, once the development has cornered the transit station, it will seek to entrap the resulting pedestrian flows within a spiderweb of passages. As Chris DeWolf writes:

Last month, a survey of 657 Tsim Sha Tsui pedestrians conducted by urban design watchdog Designing Hong Kong revealed that 77 percent prefer using street-level crossings over footbridges and subways… “The problem is that bridges and tunnels force you into particular routes that limit your ability to take the shortest path,” says Designing Hong Kong convenor Paul Zimmerman. “People also pick attractive routes. That’s a very qualitative statement, but part of what makes a route attractive is being able to see other people, to window shop, to have an experience. With subways and footbridges that becomes quite limited.”

An early version of this phenomenon can be seen in Montreal’s underground city, the most valuable retail frontage is as close to the train platforms as possible. Thus (almost as in casinos) the developers twist and turn the corridors to herd people past the shops. Future iterations of the phenomenon will soon be unveiled at the World Trade Center mall and at Hudson Yards.

Edit 7 Jul 18: author Marion Girodo has a book of “urban mangroves,” the multilevel urbanism that crops up around metro stations in Montreal, Paris, and Singapore.

Edit 17 Jan 17: Henry Grabar in Gothamist writes of “the oculus”: “If Grand Central is a train station with some shops, the Oculus is a shopping center with some trains.”

Want to get to the PATH, or cross West Street to get to the Hudson? You’ll have to walk down this hall, and oh by the way there are plenty of shopping opportunities.

The decision to elevate the stations — a far less expensive approach than burying them — may well presage this sleek new world of elevated plazas and public areas, disconnected from the ground. A new office building across from the Tysons Corner station is built atop a parking garage, so that at ground level one faces a seemingly impenetrable plinth. Already, a web of pedestrian bridges — some built by Metro, others by private developers — is emerging, keeping us safely above the world of machines and hydrocarbons and asphalt…

One wonders if you will emerge from these stations with [a] sense of pleasant surprise and rootedness in the urban landscape… Likely not. Rather, you will emerge, slightly disoriented by the ever sameness of the commercial and physical space around you, wondering for a moment if you have arrived at the right station, before your basic sense of purpose — to get home, to find a restaurant, to locate a shop — kicks in, and you begin to move by habit and instinct through a pleasantly unobtrusive world of concrete and glass that could be anywhere.

Tysons Corner Center’s “Metro Plaza” under construction. At left, the bridge to the station, at right, the bridge to the mall.

At Tysons Corner Center, the megamall at the heart of Tysons, building a bridge keeps the distance from station to mall is 300 feet — a 1.6 minute walk. The bridge siphons customers directly into the mall, creating tremendous value in three dimensions: “You’ve got a first floor on the first floor and a first floor on the second floor, so you’ve solved the verticality problem” [of pulling mall foot traffic from the entry to different levels], Timothy Steffan, an executive for mall owner Macerich, told the Post’s Jonathan O’Connell.

This Disney-esque strategy of spiriting people directly into an immersive environment has ample precedent: in fact, Roppongi Hills, a fantastically successful redevelopment in the heart of Tokyo, also uses an elevated plaza to deliver customers from the subway onto the development’s podium. The experience for customers who drive in is akin to what Rick Caruso’s malls or skyway’d downtowns provide: parking garages deadening the street environment all around, but a fantastic public space within. Sure, bus and bike customers have to deal with an ugly exterior, but the privileged modes (driving and heavy rail) get the red carpet.

Skyway urbanism in Dallas

My first instinct is to warn “creative” policymakers to be careful what you wish for: these projects result in such high cost and complexity that the only financially worthwhile result is a giant mall. They’re so huge, boring, and bland because of private value capture. Finding room in a private developer’s pro forma to build expensive underground rail infrastructure requires selling stupendous quantities of expensive corporate real estate, which will never be cool and lively. It also requires generous, greenfield-esque parcel sizes. In the worst case scenario, the project fails, and there’s nothing worse than a white elephant in the middle of the room.

Yet as dispiriting as these initial examples are, there’s a glimmer of hope that they’ll eventually be okay. With enough time, enough density, and enough owners, even these bland malls could evolve into something interesting. Hong Kong’s experience shows how the weird linkages that result from generations of ad-hoc decisions and relentless foot-traffic flows have created a hyper-dense end result that can be beautifully complex in a postmodern, emergent-urbanism way. This isn’t immediately apparent from the workaday commercial architecture, but can be mesmerizing when expressed in diagram form — as the recent book Cities Without Ground shows (high-res image slideshow). A two-dimensional plan, or even a figure-ground diagram, is useless when expressing vertical spaces.

Hong Kong architect Peter Cookson Smith described this structure in more essentialist terms in The Urban Design of Impermanence (pg. 84; excerpt):

A cityscape of streets, internalized routes and multi-level links, even without clear articulation, is open to casual exploration, and there is little need for city form to be overly organized or pronounced in order to be legible… This underlines an essential difference between the formal framework of Western public spaces and the more diffused and informal realm of social space associated with the Hong Kong street, where the relationship between public and private spaces is less tangible, and the routes between them work just as effectively in three dimensions as in two.

Perhaps China’s homogeneity and sheer density (bear in mind this is about 1-2 orders of magnitude higher than urban America’s) might increase social trust and thus break down the hierarchy of spaces — people there feel more comfortable wandering down dark alleys. Yet perhaps we could shortcut to that future: emerging spatial technologies, like smartphone-based mapping, are quickly obviating highly legible spatial hierarchies. Customers can now just as easily find a shop hidden in the back corner of a buildings as one that shouts its presence with highway-sized signs.

The PATH is a mall, first and foremost. Beyond access to over half a dozen food courts, at least two massage parlours, and more sushi restaurants than I cared to count, I put it to you that, with its existing wayfinding system still in place, the PATH offers nothing especially preferable over supra-terranean navigation… It is a seemingly endless maze of mall corridors, hallways, and atriums. Unless you are a person for whom the distinctions between Jamba Juice and Jugo Juice are particularly meaningful, everything in this place feels exactly the same; with each new tunnel you encounter in here, the space expands physically while being visually constricted. Because this space lacks the distinctive landmarks that you often find above ground, there is very little to distinguish it from every other mall you’ve been in. The more of it you explore, the less it feels like you could ever remember any of it…

The balance between mall and transit network is slanted heavily towards the PATH’s commercial interests; the dominant incentive of the landowners is to keep you in their slice of the PATH, not to move you through efficiently.

The entrance to ye olde Public Parking lies immediately beyond ye ancient Bank Drive Thru… Jokes aside, Colonial Williamsburg’s Merchants Square is an interesting 1930s-era transitional exercise in proto-shopping center design. As the site’s National Register nomination notes, this development largely explains why early shopping centers on the East Coast adopted a “Colonial” dress with red bricks, white columns, and pitched roofs. I wish that more of the era’s shopping centers had taken its lead in planning, rather than architecture, and moved the parking from in front to mid-block.

On a recent visit, it was surprising to see how far retail has sprawled around Williamsburg — exacerbated, no doubt, by sales-tax revenue rivalry between the City of Williamsburg and the surrounding James City County. Yet many of the new “lifestyle shopping villages” at the outskirts, namely New Town and High Street, suffer from subpar locations and high vacancy rates, and none has emerged as the Class A champion. I wonder how a less conservatively managed Merchants Square could have grown by just one or two more blocks north or south, adapting to the town’s growing and changing clientele of students, local residents, and tourists. Alas, we will never know.

This little scrap of the old atrium railing is within a tiny elevator lobby off M Street, next to Forever 21. The elevator is apparently used for Anthropologie’s loading and for its offices, but also has stops on floors that have been abandoned. One of the mall’s skylights is also intact, above the cash/wrap at H&M.